1. Field of the Invention
The present invention relates to an improved method of fine pounding or crushing solid particles of brittle materials in particular of solid particles of brittle mineral materials comprising a selective disaggregation and a system for carrying out the method.
2. Description of the Prior Art
With brittle materials are understood those materials which would break under the action of mechanical forces into smaller fragments even if a resilient deformation would occur before the breakage. The plastics materials which are deformed essentially without any breaking are therefore discarded from this definition.
They have already been proposed to finely crush (grind or mill) more or less coarse solid particles of brittle solid materials by using various devices, in particular crushers or grinding mills with a slow compression such as crushing rolls as disclosed for instance in the French patent specifications Nos. 2,610,540; 2,628,412 and 2,634,402 or also roller mills or some ball-mills which also are leading to the building up of agglomerates or like clusters. The pounding of load or batch particles within these appliances is indeed attended by an agglomeration or clustering of fine particles obtained as aggregates or agglomerates which it is then necessary to dissociate by a subsequent mechanical contribution the strength of which is usually less than that applied during crushing/agglomeration. For that purpose it is possible to use a ball-mill, a distributing sole plate pneumatic separator set or a gauging separator. One may also use an apparatus having a disaggregation action only (European patent specification No. 84,383 and French patent specification No. 2,616,359).
It is also known from these two last documents to recycle one part of the products issuing from the crusher to this same crusher either as such or after a simple mechanical or aeraulic sifting or screening (only those particles or agglomerates which are refused by the sieve are then recycled) or at last after the disintegration and sifting (only non-broken or insufficiently broken particles and not agglomerates since the latter have been disintegrated are then recycled).
With a view to simplify the process and the system one of the inventors has also disclosed and used a system comprising crushing rolls associated with a well performing disaggregation device for the fine pounding, the said disaggregation device being preferably integrated into the separator allowing to select the finished product leaving the pounding system (M. PALIARD-F. COCHET : "Zement, Kalk, Gips", 2, 1990, pages 71 to 76).
In the system thus described the disaggregation device has been chosen as having very good performance data (disaggregation rate of 80 to 85%) for allowing to extract at each passage the greatest possible amount of finished product. The working of the system has shown that this would result in a substantial power consumption for the disaggregation alone and in difficulties to produce the finest cements.